The invention relates to an intra-aortic balloon pump which is inserted into the aorta of a patient to assist in the functioning of a heart.
The art relating to such intra-aortic balloon pump is disclosed in U.S. Pat. No. 4,327,709, U.S. Pat. No. 4,362,150 and U.S. Pat. No. 4,422,447, for example. Known intra-aortic balloon pumps can be categorized into a surgical type and a percutaneous type. A relatively thick tube is present inside the balloon of the former type, which therefore cannot be folded into a smaller configuration, and hence a surgical operation is required to insert it into the aorta of a patient. A balloon pump of the latter type can be reduced in its profile by folding or wrapping it, and thus can be inserted into the aorta without requiring a surgical operation. This simplifies the handling of a balloon pump of percutaneous type during its mounting and dismounting in a preferable manner.
One example of an intra-aortic balloon pump of the percutaneous type is illustrated in FIG. 3a. In this Figure, one end of a balloon 24 is connected to one end of a tubular member (catheter) 22 to provide a communication between the internal spaces of the both members. The other end of the balloon 24 is supported by one end of a central wire 23 which is disposed within the member 22. The internal space of the member 22 is in communication with a drive port 20. Accordingly, a desired drive unit may be connected to the port 20 to apply a positive and a negative pressure thereto alternately, thus enabling the balloon 24 to inflate and deflate alternately and repeatedly. Thus, when a positive pressure is applied, a drive fluid such as helium gas, for example, passes through the internal space of the member 22 to enter the balloon 24, the internal space of which is expanded, thus expanding or inflating the balloon. In response to the application of negative pressure, the drive fluid within the balloon 24 is displaced therefrom through the member 22 to flow out of the port 20, thus deflating the balloon 24. A poor functioning heart can be assisted by performing such inflating and deflating motion in synchronism with the beating motion of the heart of a patient.
In an intra-aortic balloon pump as illustrated in FIG. 3a, it is to be noted that during its deflating motion, the balloon 24 tends to begin its deflation in a region adjacent to a catheter opening 22a earlier than the distal end thereof, as illustrated in FIG. 3b. It will be noted that the balloon 24 requires a further deflating motion under the condition illustrated in FIG. 3b. However, the contraction of part of the balloon 24 reduces the fluid channel providing a communication between the internal space of the balloon 24 and the catheter opening 22a, thereby standing in the way of the effluence of the fluid. Accordingly, such phenomenon tends to retard the deflating motion of the balloon.
This phenomenon has been observed using an experimental apparatus illustrated in FIG. 4a which is used to determine a change occurring in the pressure. An intra-aortic balloon pump is shown at BLN which is driven by a drive unit 30. In order to load the balloon pump BLN, it is immersed into a water vessel 40. The drive unit 30 comprises a compressor 31 which produces a positive pressure, a vacuum pump 33 which produces a negative pressure, solenoid valves 32, 34, an isolator 35 and a controller 37. The drive unit 30 is designed to produce a positive and a negative pressure alternately, whereby there occurs a movement of a fluid in a direction indicated by a double-headed arrow AR2 within a tube which interconnects the drive unit 30 and the balloon pump BLN.
FIG. 4b graphically shows a secondary pressure P1 of the isolator and a pressure P2 which prevails within the balloon pump, both of which are obtained using the arrangement mentioned above. In FIG. 4b, a systole is indicated at T1 and a diastole is shown at T2. During the systole, the balloon pressure P2 should theoretically change with a constant decline as indicated by broken lines, but in actuality, the rate of decline is reduced at a point where the pressure has been reduced to one-half the initial value, thus retarding a reduction in the pressure. It is considered that this is caused by the contraction of part 24a of the balloon to reduce the fluid channel between the balloon and the central wire 23, presenting an increased resistance to the flow of fluid in such region.
Such retardation of the inflating motion is inherent in the construction of the percutaneous balloon. In a balloon of the surgical type, a portion thereof which corresponds to the central wire is formed by a relatively thick, hollow member having a multiplicity of openings in its periphery which permit a fluid flow. Accordingly, a balloon pump of surgical type does not suffer from a restricted effluence of fluid from the rest of the balloon due to the contraction of part thereof which occurs first. However, it is of course recognized that a surgical operation of a patient is required to use a balloon pump of surgical type.
The purpose of an intra-aortic balloon pump is to assist in the pulsation of a heart by causing the balloon to deflate with a timing which is determined by the pulsation of the heart to reduce the blood pressure within the aorta. However, when the heart rate increases to an abnormally high value, or an unpredictable pulsation occurs due to the arrhythmia, a failure of the balloon to deflate rapidly causes the likelihood that the presence of the balloon itself may interfere with the pulsation.
An approach which accommodates for such difficulty is disclosed in U.S. Pat. No. 4,515,587 wherein a corrugated resilient member is disposed between the internal spaces of the catheter and the balloon in a displaceable manner so that when inserted into the balloon, the resilient member prevents a local collapse of the balloon during its deflating motion. However, this still involves the following difficulties:
1. When the resilient member is expelled into the balloon from the catheter tube, it is located within a patient and hence is invisible by an operator, who therefore must rely on his experience and skill in positioning the resilient member. Thus, a balloon pump of this kind requires a high level of skill and is very difficult to operate.
2. It is necessary to expel the resilient member into the balloon from the catheter tube immediately after the balloon pump has been inserted into the physical body of a patient, and to remove the resilient member from the balloon into the catheter tube before the balloon pump is to be removed. Thus, the mounting and dismounting operation of the balloon pump is troublesome and requires an extended length of time.